Intervertebral implant and associated method

ABSTRACT

An intervertebral implant and associated method. The intervertebral implant can include a first component having a first articulating surface and a first bone engagement surface for engaging a first vertebra, and a second component having a second articulating surface and a second bone engagement surface for engaging a second vertebra adjacent to the first vertebra. The first and second articulating surfaces can articulate with each other for substantially replicating a natural spinal movement. The first and second bone engagement surfaces can define an outer surface substantially shaped as an envelope of two intersecting cylinders. In one aspect, the first and second articulating surfaces can have substantially equal radii of curvature in a coronal plane and different radii of curvature in a sagittal plane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/567,272 filed on Dec. 6, 2006, which is a continuation-in-part ofU.S. patent application Ser. No. 11/248,101 filed on Oct. 12, 2005claiming the benefit of U.S. Provisional Application No. 60/619,842,filed on Oct. 18, 2004. The disclosures of the above applications areincorporated herein by reference.

INTRODUCTION

The spinal column provides the main support for the body and is made ofthirty-three individual bones called vertebrae. There are twenty-fourmoveable vertebrae in the spine, with the remaining being fused. Eachvertebra includes an anterior vertebral body, a posterior vertebral archthat protects the spinal cord, and posterior processes extending fromthe vertebral arch. The vertebral body is drum-shaped and includessuperior and inferior endplates. The moveable vertebrae are stacked inseries and are separated and cushioned by anterior intervertebral discs.

Each vertebral body transmits loads to adjacent bodies via an anteriorintervertebral disc and two posterior facets. The intervertebral disc iscomposed of an outer fibrous ring called the annulus. Nucleus pulposusis a gel-like substance housed centrally within the annulus andsandwiched between the endplates of the adjacent vertebral bodies. Theannulus operates as a pressure vessel retaining an incompressible fluid.In a healthy disc, the nucleus pulposus acts as hard sphere seatedwithin the nuclear recess (fossa) of the vertebral endplates. Thissphere operates the fulcrum (nuclear fulcrum) for mobility in the spine.Stability is achieved by balancing loads in the annulus and the facetjoints.

Degenerative disc disease affects the physiology of the disc and may becaused by aging, protrusion of the nucleus into the annulus orendplates, trauma or other causes. The result in either case may producea reduction of disc height, which, in turn, alters the loading patternin the facets causing symptomatic degeneration of the facet joints, thusreducing stability, and compressing nerves branching out of the spinalcolumn.

Examples of surgical treatments of degenerative disc disease includespinal arthroplasty with total disc replacement that requires a fulldiscectomy or with nucleus replacement that disrupts the annulus.Although these devices can be effective for their intended purposes, itis still desirable to have implants and associated methods that are lessdisruptive and provide the required degree of stability and mobility tothe affected region of the spine.

SUMMARY

The present teachings provide an intervertebral implant and associatedmethod. The intervertebral implant comprises superior and inferiorcomponents mutually articulating to replicate natural spine movement.

In one aspect, the present teachings provide an intervertebral implantthat can include a first component having a first articulating surfaceand a first bone engagement surface for engaging a first vertebra, and asecond component having a second articulating surface and a second boneengagement surface for engaging a second vertebra adjacent to the firstvertebra. The first and second articulating surfaces can articulate witheach other for substantially replicating a natural spinal movementincluding torsion, extension/flexion, and lateral bending. The first andsecond bone engagement surfaces can define an outer surfacesubstantially shaped as an envelope of two intersecting cylinders.

In one aspect the first and second articulating surfaces can havesubstantially equal radii of curvature in a coronal plane and differentradii of curvature in a sagittal plane. In another aspect, the firstarticulating surface can include a convex portion in the coronal planeand a concave portion in the sagittal plane, and the second articulatingsurface can include a concave portion in the coronal plane and convexportion in the sagittal plane.

The present teachings provide a surgical kit that includes an insertioncannula defining a longitudinal bore, an intervertebral implantpre-loaded within the longitudinal bore, and a retainer for temporarilyretaining the intervertebral implant within the longitudinal bore.

The present teachings also provide a method for inserting anintervertebral implant in a disc space. The method includes providing aninsertion cannula having a longitudinal bore, preloading theintervertebral implant within the longitudinal bore of the insertioncannula in a substantially fixed position, supporting the insertioncannula relative to the disc space, releasing the intervertebral implantfrom the substantially fixed position, and implanting the intervertebralimplant into the disc space.

The present teachings also provide a surgical device that includes aninsertion cannula defining a longitudinal bore and a retainer integralto the cannula, an intervertebral implant matingly pre-loaded within adistal portion of the longitudinal bore and releasably held by theretainer.

The present teachings further provide a surgical device that includes amodular intervertebral implant having an outer surface substantiallyshaped as an envelope of five cylinders.

The present teachings further provide a spacer guide adapted forsupporting a plurality of tools used for preparing vertebral endplatesfor receiving an intervertebral implant. The spacer guide can include atool-supporting elongated shaft, a depth stop flange at a distal portionof the shaft, wherein the flange defines a plurality of guiding cutoutsfor guiding the plurality of tools, and a frame extending from theflange and receivable into the intervertebral disc space. The frame caninclude a distal member operable as a stop for the plurality of tools.

The present teachings also provide a cutting tool guide for vertebralendplates for receiving an intervertebral implant. The cutting toolguide can include a cannulated body defining a plurality of guidingbores, wherein each guiding bore is configured for supporting a cuttingtool used to prepare an opening in the endplates for receiving acorresponding portion of the intervertebral implant. The cutting toolguide can include a boss extending distally from the body. The boss caninclude a plurality of guiding grooves aligned with the correspondingbores of the body.

Further areas of applicability of the present invention will becomeapparent from the description provided hereinafter. It should beunderstood that the description and specific examples are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a sagittal sectional view of an intervertebral implantaccording to the present teachings, shown implanted in a spine;

FIG. 1A is a coronal end view of an intervertebral implant according tothe present teachings, shown implanted in a spine;

FIG. 2 is a coronal end view of a toroidal intervertebral implantaccording to the present teachings;

FIG. 3 is an isometric view of the intervertebral implant of FIG. 2;

FIG. 4 is a coronal end view of a spherical intervertebral implantaccording to the present teachings;

FIG. 5 is an isometric view of the intervertebral implant of FIG. 4;

FIG. 6 is a coronal end view of an intervertebral implant according tothe present teachings;

FIG. 7 is an isometric view of the intervertebral implant of FIG. 6;

FIG. 8 is a side view of a probe shown in use for locating a nuclearrecess;

FIGS. 9A, 9B and 9C illustrate exemplary articulation motions includingtorsion, extension/flexion, and lateral bending, respectively, for atoroidal intervertebral implant according to the present teachings;

FIG. 10 is an isometric view of an intervertebral implant according tothe present teachings, shown implanted;

FIG. 11 is a sagittal sectional view of the intervertebral implant ofFIG. 10;

FIG. 12A is an isometric view of a superior component of a toroidalintervertebral implant according to the present teachings;

FIG. 12B is a coronal sectional view of the superior component of thetoroidal intervertebral implant of FIG. 12A;

FIG. 12C is an axial view of the superior component of the toroidalintervertebral implant of FIG. 12A;

FIG. 12D is a sagittal sectional view of the superior component of thetoroidal intervertebral implant of FIG. 12A;

FIG. 13A is an isometric view of an inferior component of a toroidalintervertebral implant according to the present teachings;

FIG. 13B is a coronal sectional view of the inferior component of thetoroidal intervertebral implant of FIG. 13A;

FIG. 13C is an axial view of the inferior component of the toroidalintervertebral implant of FIG. 12A;

FIG. 13D is a sagittal sectional view of the inferior component of thetoroidal intervertebral implant of FIG. 13A;

FIG. 14 is a conceptual illustration of constructing a toroidalintervertebral implant according to the present teachings;

FIGS. 15A, 15B and 15C illustrate exemplary articulation motions for aspherical intervertebral implant according to the present teachings

FIG. 16A is a sagittal sectional view of a spherical intervertebralimplant according to the present teachings;

FIG. 16B is a coronal sectional view of the spherical intervertebralimplant of FIG. 16A;

FIG. 17A is an isometric view of an intervertebral implant according tothe present teachings;

FIG. 17B is a front view of an intervertebral implant according to thepresent teachings;

FIG. 17C is a side view of an intervertebral implant according to thepresent teachings;

FIG. 17D is a sectional view of the intervertebral implant of FIG. 17A,taken along axis 17D;

FIG. 17E is a sectional view of the intervertebral implant of FIG. 17A,taken along axis 17E;

FIGS. 18-30 illustrate a method of implanting an intervertebral implantaccording to the present teachings;

FIG. 31 is a side view of a clip holding an intervertebral implant in aninsertion cannula according to the present teachings;

FIG. 32 is a view of a clip holding an intervertebral implant in aninsertion cannula according to the present teachings;

FIG. 33 is a plan view of a distraction pin guide according to thepresent teachings;

FIG. 34 is a sectional view of a cutting tool guide cannula according tothe present teachings;

FIG. 35 is a frontal view of an intervertebral implant according to thepresent teachings, shown implanted in a spine;

FIG. 36 is a frontal view of an intervertebral implant according to thepresent teachings,

FIG. 37 is an isometric view of the implant of FIG. 36;

FIG. 38 is a side view of the implant of FIG. 36;

FIG. 39 is a top view of the implant of FIG. 36;

FIG. 40 is another isometric view of the implant of FIG. 36;

FIG. 41 is an environmental view of a disc sizer according to thepresent teachings;

FIG. 42 is an isometric view of the disc sizer of FIG. 41;

FIG. 43 is an environmental view of a spacer guide according to thepresent teachings;

FIG. 44 is an isometric view of the spacer guide of FIG. 43;

FIG. 45 is an environmental isometric view illustrating drilling acentral hole for the implant according to the present teachings;

FIG. 46 is an environmental isometric view illustrating drilling fourholes for the implant according to the present teachings;

FIG. 47 is an isometric view of a drilling guide according to thepresent teachings:

FIG. 48 is an environmental isometric view illustrating inserting animplant according to the present teachings; and

FIG. 49 is an isometric view of an insertion cannula according to thepresent teachings.

DESCRIPTION OF VARIOUS ASPECTS

The following description is merely exemplary in nature and is in no wayintended to limit the invention, its application, or uses. For example,although the present teachings are illustrated for intervertebral discimplants, the present teachings can be used for other spine implants,such as intervertebral spacers, for example.

Referring to FIGS. 1 and 1A, exemplary intervertebral implant 100,according to the present teachings are illustrated as implanted betweentwo adjacent vertebral bodies 80 having endplates 84. The intervertebralimplant 100 can be nested between the endplates 84 of the vertebralbodies 80 and may be partially surrounded by a portion of a naturalintervertebral disc 82 replacing the nucleus thereof. Alternatively, theentire natural intervertebral disc 82 can be removed and replaced by theintervertebral implant 100.

The intervertebral implant 100 can be a multiple component implant thatincludes superior and inferior components 102, 104 configured for mutualarticulation that can replicate the primary modes of motion in the spineand any combination thereof. The superior and inferior articulationcomponents 102, 104 can be designed to resurface the adjacent endplates84 at the nuclear fulcrum and re-establish disc height to its originaldimension. Accordingly, improved motion and increased stability can beestablished in the region of the intervertebral implant 100 withoutdependence on the integrity of the endplate cartilage.

The articulation between the inferior and superior articulationcomponents 102, 104 of the intervertebral implant 100 can substantiallyreplicate natural spinal movement. Two exemplary aspects of sucharticulation between the inferior and superior articulation components102, 104 of the intervertebral implant 100 are illustrated in FIGS. 3and 5, and referred respectively herein as “toroidal” and “spherical”intervertebral implant 100 for reasons that are discussed below. Thearticulation illustrated in FIG. 1A, and FIGS. 17A-17C is of thespherical type, although toroidal type articulation can also be usedwith the intervertebral implant 100 illustrated in these figures.

More particularly, FIGS. 9A, 9B, and 9C illustrate respectively torsion,extension/flexion, and lateral bending for the toroidal intervertebralimplant 100 of FIG. 3, and FIGS. 15A, 15B, and 15C illustraterespectively torsion, extension/flexion, and lateral bending for thespherical intervertebral implant 100 of FIG. 5.

Referring to FIGS. 3 and 5, each of the superior and inferior components102, 104 can include a serrated rack 106 for preventing migration of theintervertebral implant 100 relative to the vertebral bodies 80. It willbe appreciated that other anchoring structures known in the art can beused for securing the intervertebral implant 100 against migration, suchas, for example, projections of various geometric shapes engagingcorresponding recesses in the endplates, surface treatment promotingfrictional resistance including porous coatings that promote bonegrowth, and other structures.

Referring to FIGS. 2, 3, and 12-14, the toroidal intervertebral implant100 can be created, for example, by removing a cylinder at the contactbetween two tori 90, 92, as conceptually illustrated in FIG. 14.Referring to FIG. 12C, the superior component 102 includes anarticulating surface 110. The articulating surface 110 of the superiorcomponent 102 includes a convex radius in the coronal plane, as shown inFIG. 12B, and a concave radius in the sagittal plane, as shown in FIG.12D. Referring to FIG. 13C, the inferior component 104 includes anarticulating surface 120. The articulating surface 120 of the inferiorcomponent 104 includes a concave radius in the coronal plane, shown inFIG. 13B, and a convex radius in the sagittal plane, shown in FIG. 13D.In the sagittal plane, the superior articulating surface 110 can have alarger radius of curvature than the inferior articulating surface 120.In one aspect, in the coronal plane, the convex superior articulatingsurface 110 can be defined by a shallow “V” having a tip that is roundedwith a fillet radius. The toroidal intervertebral implant 100 caninclude an A/P taper to minimize subchondral bone removal.

Referring to FIGS. 4, 5, and 16, the superior and inferior components102, 104 of the spherical intervertebral implant 100 include respectivearticulating surfaces 130, 132. The articulating surface 132 of theinferior component 104 is convex and at least partially spherical. Thearticulating surface 130 of the superior component 102 is concave. Inthe sagittal plane, shown in FIG. 16A, the radius of the superiorcomponent 102 can be greater than the radius of the inferior component104 to allow for anterior-posterior (A/P) translation. The apex of thearticulating surfaces 130, 132 is indicated by axis A-A in FIG. 16A, andcan be offset two thirds posteriorly to align the articulating fulcrumof the spherical intervertebral implant 100 with the nuclear recess inthe vertebral endplates 84. The radius of curvature of the inferiorarticulating surface 132 can be larger anteriorly to the apex (axis A-A)than the radius of curvature posteriorly to the apex, as illustrated inFIG. 16A. The spherical intervertebral implant 100 can include an A/Ptaper to minimize subchondral bone removal. In the coronal plane, shownin FIG. 16B, the curvatures of the articulating surfaces 130, 132 arecongruent with equal radii to maximize contact area.

The intervertebral implant 100 illustrated in FIGS. 1A, and 17A-17E, canhave a spherical or toroidal type of articulation, as discussed above,although spherical articulating surfaces 301, 303 are illustrated, asshown in the sectional views of FIGS. 17D and 17E. The superior andinferior articulating components 102, 104 can include respectivesuperior and inferior bone engagement surfaces 305, 309. The superiorand inferior bone engagement surfaces 305, 309 can include pairs ofseparate outwardly convex end portions 306, 308 connected with outwardlyconcave intermediate portions 304, 310, respectively. The superior andinferior bone engagement surfaces 305, 309 can be formed, for example,by two cylinders 306 a, 306 b of circular cross-section, which can beintersecting, as illustrated in FIG. 17B in dotted lines. Accordingly,the outer surface 101 of the bi-cylindrical intervertebral implant canbe defined as a curved surface enveloping the intersecting cylinders 306a, 306 b. Non-intersecting cylinders can also be used in other aspects.

Each of superior and inferior bone engagement surfaces 305, 309 caninclude bone-engagement formations 302. The bone engagement formations302 can be arranged in parallel rows on the convex end portions 306,308. The engagement formations 302 can include crests 312 and grooves314. Both crests 312 and grooves 314 can be designed with smooth roundedprofiles balancing effective bone engagement while reducing potentialdamage by avoiding sharp edges.

The intervertebral implant 100 can be manufactured from biocompatiblematerials, such as, for example, cobalt chromium alloy, titanium alloysor other metals, pyrolytic carbon, and other materials. It can also beconstructed from a combination of materials. Referring to FIGS. 6 and 7,each superior component 102 can include an outer portion 101 made oftitanium, titanium alloy or other biocompatible metal or alloy, and anarticulating portion 103 made of pyrolytic carbon. Similarly, eachinferior component 104 can include an outer portion 105 made oftitanium, titanium alloy or other biocompatible metal or alloy, and anarticulating portion 107 made of pyrolytic carbon. It should be notedthat although the intervertebral implant 100 illustrated in FIGS. 6 and7 is of the spherical type, the toroidal intervertebral implant 100 canalso be manufactured by a similar combination of materials. It will beappreciated that other biocompatible metallic or non-metallic materialscan also be used.

It will be appreciated that the terms “toroidaI” and “spherical” are inreference to the relative articulation of the superior and inferiorcomponents 102, 104, and that the overall shape of the intervertebralimplant 100 can be substantially cylindrical, as illustrated 2, 3 and 6,or bi-cylindrical, as illustrated in FIGS. 17A-17E. Referring to FIGS.2, 3, and 6, the coronal section of the intervertebral implant 100 caninclude a substantially circular central section defined by the superiorand inferior components 102, 104 and two partially circular extensionsdefined by the serrated racks 106. It will be appreciated, however, thatparticular features associated with particular illustrations are merelyexemplary. Accordingly, features that illustrated in one exemplaryembodiment can also be used in other embodiments, although notparticularly illustrated.

The method of implanting the intervertebral implant 100 and associatedinstruments is described with particular reference to FIGS. 18-25, andwith additional reference to FIG. 8, for implanting the intervertebralimplant 100 illustrated in FIGS. 17A-17C.

Preparatory to the surgical procedure, the patient can be positionedsuch that there is a natural amount of lordosis, if the surgeon prefersto perform a discectomy under distraction. The affected segment of thespine can be exposed anteriorly. A small annulotomy/discectomy can beperformed, excising the nucleus and all degenerated material. Referringto FIG. 18, the annulotomy/discectomy can be sized for receiving acentering shaft 320 or other centering/locating instrument, such as, forexample, a fossa locator 206 illustrated in FIG. 8. The fossa locator206 can be inserted into the natural disc space to locate the nuclearrecess 86. The fossa locator 206 can include a removable handle 208, ashaft 240 and a distal tip 242 that can be cylindrical in shape. Thefossa locator 206 can be inserted until the tip 242 engages the nuclearrecess 86. Graduated markings 220 on the shaft 240 of the fossa locator206 indicate the depth required for subsequent drilling and broaching.The handle 208 from the fossa locator 206 can then be removed, such thatthe shaft 240 of the fossa locator can also function as a centeringshaft, such as the centering shaft 320 illustrated in FIG. 18.

Referring to FIGS. 19 and 33, a distraction pin guide 322 can be placedover the centering shaft 320. The distraction pin guide 322 can includea pair of side longitudinal openings/lumens 324, 328 and an intermediatelongitudinal opening/lumen 326 positioned therebetween. The intermediatelongitudinal opening 326 can be defined by an internal wall structure327 that fully separates the intermediate opening 326 from the sideopenings 324, 328, as illustrated in FIG. 33, which shows theintermediate opening 326 and the side openings 324, 328 as threenon-intersecting circles. It will be appreciated that other wallstructures can also be used, including wall structures that allow atleast partial communication between the intermediate opening 326 and theside openings 324, 328. The centering shaft 320 can be received in theintermediate opening 326, which is appropriately sized. A pair ofself-drilling distraction pins or other anchoring pins 330 can beinserted through the side openings 322, 328 for anchoring into adjacentvertebrae on opposite sides of the disc space. The centering shaft 320and the distraction pin guide 322 can be removed after placement of thedistraction pins 330, as illustrated in FIG. 20.

Referring to FIGS. 21-30, a distractor 332 can be used for facilitatingthe implantation procedure. The distractor 332 can include a pair oftubular legs 334 and a distraction mechanism 336 for applying andcontrolling the amount of distraction, if any, desired by the surgeon.The distractor legs 334 can be placed over the pins 330, as illustratedin FIG. 21. The depth of inferior vertebral body can be measured using adepth gauge, such as the fossa locator 206 illustrated in of FIG. 8.This measurement can be used to determine the drilling depth.

Referring to FIGS. 22-27 and 34, the centering shaft 320 can be insertedinto the disc space. A drill guide cannula 338 can be positioned overthe centering shaft 320 and between the legs 334 of the distractor 332.The drill guide cannula 338 can be secured on the distractor 332 with acannula lock 340. The cannula lock 340 can include a longitudinalelement 342 defining a first opening 361 configured for receiving thedrill guide cannula 338 therethrough, and a flange 360 at an angle tothe longitudinal element 342. The flange 360 can define one or moreflange openings 344 for engaging a locking element 345, such as a thumbscrew. The drill cannula 338 can be pre-assembled in the cannula lock340 through the first opening 361, and the assembly can be placed overthe centering shaft 320. The flange 360 of the cannula lock 340 can siton the distractor 332, and the drill guide cannula 338 can be secured onthe distractor 332 by tightening the locking element 345 through one ofthe flange openings 344. The drilling depth can be measured by readingmarkings provided on the centering shaft 320 at the top of the drillguide cannula 338, as described above in connection with the fossalocator 240 illustrated in FIG. 8, and compared with the requireddrilling depth determined earlier. After the drilling depth isconfirmed, the centering shaft 320 can be removed, as shown in FIG. 24.

Referring to FIGS. 25-27 and 34, the drill guide cannula 338 can includea longitudinal opening 339 adapted for receiving the centering shaft 320for locating guidance, and other instruments, such as a drill 346 whichcan be inserted in more than one position relative to the longitudinalopening 339, as appropriate for preparing the disc space foraccommodating the overall geometry of the particular intervertebralimplant 100. For example, for the bi-cylindrical intervertebral implant100 illustrated in FIGS. 1A, and 17A-17C, the drill 346 can bepositioned in first and second positions defined by first and secondopen intersecting circles 339 a, 339 b of the longitudinal opening 339of the drill guide cannula 338, as illustrated in FIG. 34, andcorresponding to the circles 309 a, 309 b of the bi-cylindricalintervertebral implant 100 illustrated in FIG. 17B. The centering shaft320 can be received in an intermediate position defined by a thirdcircle 339 c of smaller diameter than the first and second circles 339a, 339 b, and intersecting the first and second circles 339 a, 339 b, asillustrated in FIG. 34.

In one exemplary embodiment, flat-bottomed holes having diameter ofabout 8 mm can be drilled to a depth determined as described above.Drill stops can be used to control the depth of drilling and/orbroaching. The desired depth can align the center of the intervertebralimplant 100 with the nuclear recess 86. After drilling, bone debris canbe removed by irrigation and suction, and the drill guide cannula 338can be pulled out of cannula lock 340 and completely removed, asillustrated in FIG. 27. The drill guide cannula 338 can be sized suchthat it stops short of the vertebrae defining a gap 362 between thedistal end of the cannula 338 and the vertebrae, as can be seen in FIG.26. The gap 362 can facilitate the removal of the drill guide cannula338 after drilling.

Referring to FIGS. 28-32, an elongated insertion cannula 350 can beinserted into the first opening 361 of the cannula lock 340. Theinsertion cannula 350 can be pre-loaded with the intervertebral implant100, as illustrated in FIGS. 31 and 32. The insertion cannula 350 can bemade of smooth plastic that can protect the intervertebral implant 100from scratching, for example, and can be disposable. The insertioncannula 350 can include a longitudinal bore 364. The longitudinal bore364 can be shaped to conform to, and/or otherwise accommodate the shapeof the intervertebral implant 100, for example the bi-cylindricalintervertebral implant 100, as illustrated in FIG. 31. The shape of thelongitudinal bore 364 can also maintain the relative position of thecomponents 102, 104 of the multiple-component intervertebral implant100. The insertion cannula 350 can include an enlarged tubular proximalend 366, which can provide a shoulder 368 resting on the cannula lock340 when the insertion cannula 350 is inserted through the first opening361 of the cannula lock 340.

Referring to FIGS. 28-32, the intervertebral implant 100 can be held inthe enlarged proximal end 366 of the insertion cannula 350 using aremovable retainer or other temporarily retaining device, such as a clip352, for example. The clip 352 can hold the intervertebral implant 100at a substantially fixed position within the longitudinal bore 364 ofthe insertion cannula 350, and maintain the relative positions of thesuperior and inferior components 102, 104 of the intervertebral implant100. The clip 352 can be substantially flat and can include a head 372and two compliant arms 370 extending from the head 372. The compliantarms 370 that can hold the intervertebral implant 100 at the concaveintermediate portions 304, 310 of the intervertebral implant 100 shownin FIG. 17B. The arms 370 can be received through a diametrical slot 354of the proximal end 366 of the insertion cannula 350, or otherappropriate opening thereon. The clip 352 can be inserted from theproximal end 366 of the insertion cannula 350, and can be removed bypulling out the proximal end 366. Removing the clip 352 causes the arms370 to open, thereby releasing the intervertebral implant 100 into thebore 364 of the insertion cannula 350. A plastic tamp 374 can be used topush the intervertebral implant 100 through the insertion cannula 350and into the prepared disc space, as illustrated in FIG. 30. Theinsertion cannula 350, the distractor 332 and the distraction pins 330can then be removed leaving the intervertebral implant 100 appropriatelypositioned, as illustrated in FIG. 1A.

The intervertebral implant 100 can be provided in a sterilized kit thatincludes the insertion cannula 350. The intervertebral implant 100 canbe preloaded in the insertion cannula 350 and held by the clip 352. Thetamp 374 can also be included in the kit. Kits including intervertebralimplants 100 of different sizes can be provided. After use, any of theinsertion cannula 350, the clip 352 and the tamp 374 can be disposed, orre-sterilized and re-used.

Although the method of implanting the intervertebral implant 100 andassociated instruments was described above in reference to thebi-cylindrical intervertebral implant 100 illustrated in FIGS. 17A-17C,similar procedures can be used for implanting the toroidal and sphericalintervertebral implants 100 illustrated in FIGS. 2, 4 and 6. Referringto FIGS. 10 and 11, for example, a pair of holes 230 can be drilled tothe required depth as determined by the graduated markings 220 of thefossa locator 206 for accommodating the serrated racks 106 of thetoroidal or spherical intervertebral implant 100. A central hole 232 canbe drilled per the required depth to accommodate the body of toroidal orspherical intervertebral implant 100. Similarly, the shape of thevarious implantation instruments, such as the drill guide cannula andthe insertion cannula, for example, can be designed to accommodate thetoroidal or spherical implant.

Referring to FIGS. 35-49, instruments and methods for implanting anintervertebral implant 400 according to the present teachings areillustrated. The intervertebral implant 400 illustrated in FIGS. 35-40,similarly to the intervertebral implant 100 described above, can includesuperior and inferior articulation components 402, 404 withcorresponding superior and inferior articulating surfaces 401, 403. Thearticulation surfaces 401, 403 can provide articulation of the sphericalor toroidal type, which was described above in connection with theintervertebral implant 100 and will not be repeated here. The superiorand inferior articulating components 402, 404 can include respectivesuperior and inferior bone engagement surfaces 405, 409 having boneengagement formations defined by alternating and smoothly curved crests412 and grooves 414, or other geometry corresponding to keels, pegs, orother endplate engagement structures. It will be understood that theimplant 100 can be a multiple-component implant and that each of thesuperior and inferior articulation components 402, 404 can be modularincluding separate endplate engagement and articulation portions asdiscussed in connection to the implant 100 shown in FIGS. 6 and 7.

The curved outer surface of the intervertebral implant can be defined asthe envelope of five intersecting cylinders including a central cylinder406 a and four smaller corner cylinders 406 b, as shown in FIG. 36. Thefive cylinders 406 a, 406 b can all have circular cross-sections.Non-intersecting cylinders can also be used as well. Accordingly, eachof the superior and inferior bone engagement surfaces 405, 409 caninclude three cylindrical portions defined by the outer portions ofcylinders 406 a and 406 b.

An exemplary method of implanting the intervertebral implant 400 and theassociated instruments is described with particular reference to FIGS.41-49. Preparatory to implantation, a complete discectomy can beperformed, including removal of any overhanging osteophytes. The depthof the vertebral bodies 80 can be measured using a conventional depthgauge for determining the depth of insertion of the implant 400, or byany other method known in the art.

Referring to FIGS. 41 and 42, a series of disc-sizers 500 of differentheights can be used to evaluate the height of the disc space. Anexemplary disc sizer 500 can have an elongated shaft 502 and a distalplate-like tip 504 that can have a convex superior surface 506 and asubstantially but not completely flat inferior surface 508 defininghaving a maximum distance or height “H” therebetween. The shape of thedistal tip 504 can mate to the natural surfaces of the endplates 84 suchthat the highest portion of the disc space at the center of the nuclearrecess can be measured. The operating surgeon can first try a small discsizer 500 having a distal tip 504 of small height H, and thensequentially use disc sizers 500 with increasing height H until a closefit can be achieved. The disc sizer 500 can include a plate-like stopmember 510 at a predetermined distance from the distal tip 504 andsubstantially perpendicular to the shaft 502 of the disc sizer 520. Thestop member 510 can prevent the disc sizer 500 from going too deeply andinjuring the spinal cord, if a too-small disc sizer is used. The stopmember 510 can also be adjustable.

Referring to FIGS. 43 and 44, an appropriately sized spacer guide 520can be inserted into the disc space. The spacer guide 520 can be used asa starting base for making a central hole and four corner holescorresponding to the five cylinders 406 a, 406 b that define geometry ofthe implant 400. The depth of insertion “D” of the spacer guide 520corresponds to the depth determined by the depth gauge, and thethickness/height “H” correlates to the size determined by the disc sizer500, as described above. The spacer guide 520 can include an elongatedshaft 522 over which various cannulated drills can be placed to preparethe endplates 84 for receiving the implant 400, as discussed below. Thespacer guide 520 can include a depth stop flange 524 substantiallyperpendicular to the shaft 522. The flange 524 can abut against theanterior face of the vertebral bodies 80 to stop the spacer guide 520 atthe appropriate depth D. The flange 524 can have a central cutout 528 aand four smaller tool-guiding cutouts 528 b at the four corners forallowing passage of drills or other cutting tools that can be used toprepare the endplates 84 for receiving the implant 400. For example, thefour corner cutouts 528 b can receive drills for making holescorresponding to the cylinders 406 b of the implant 400, shown in FIG.36. The central cutout 528 a can receive a drill for making a centralhole corresponding to the central cylinder 406 a of the implant 400.Accordingly, the periphery defined by the cutouts 528 a, 528 b,generally or collectively referenced as cutouts 528, can correlate tothe size and outer shape of the implant 400 for guiding various cuttingtools that prepare the vertebral endplates 84 for receiving theintervertebral implant 400. It will be appreciated that the spacer guide520 can be similarly used with other instruments for cutting bone inaddition to drills, such as, for example, reamers, rasps, punches andchisels. Further, the spacer guide 520 need not be limited for use withthe particular geometry of the intervertebral implant 400, but can alsobe used for other implant geometries, such as, for example, the implantsidentified by reference numbers 100 hereinabove. Accordingly, the flange524 can have tool-guiding cutouts 528 a/528 b of different shapes andlocations along the flange 524 for guiding instruments corresponding tokeels, pegs and other anchoring devices of the implant. For the implant100 shown in FIG. 4, for example, the flange 524 can have two centralcutouts corresponding to the racks 106 or other keels or pegs forengaging the endplates 84 of the vertebral bodies 80. Similarly, theflange 524 can include cutouts 528 corresponding to the engagementformations 312 of the implant 100 shown in FIG. 17A.

The spacer guide 520 can also include a depth stop frame member 526 thatcan extend into the disc space and can also serve as a hard stop for thedrills. The frame member 526 can have a substantially planar U-shapethat extends from the flange 524 to the distal end of the shaft 522. Theframe member 526 can also be tapered for ease of insertion. The framemember 526 can be substantially perpendicular the flange 524 and canhave height H, as shown in FIG. 44. The frame member 526 can include twoarms 530 connected with distal member 532 that provides a stop fordrills. The angle defined by the distal member 532 and each of the arms530 can be chamfered or tapered or rounded, and can also be less than 90degrees. The distal member 523 can also have a tapered or angledcross-section for facilitating insertion. The arms 530 can be parallelor can be inclined defining a tapering providing for lordosis. The arms530 of the frame member 526 can have serrations or teeth or othertexturing on the arm surfaces that contact the inferior and superiorsurfaces of the vertebral bodies 80 to help stabilize the spacer guide520 in the disc space. The spacer guide 520 can be made in many sizesthat provide a variety of heights H for each depth D and size of implantcombination such that a snug fit can be achieved in the disc space.

Referring to FIG. 45, a cannulated drill 540 can be placed over theshaft 522 of the spacer guide 520 to prepare a center hole thatcorresponds to the diameter of the central cylinder 406 a of the implant400. A series of different diameter drills 540 of sequentiallyincreasing diameters can be used until the final diameter is reached.Bone debris from drilling can be removed by irrigation and suction, aswell as by the geometry of the cutting instruments.

Referring to FIGS. 46 and 47, a cutting tool guide 550 for the cornerholes can be placed over the spacer guide 520. The cutting tool guide550 can include a body 552, a distal flange 554 and a boss 570 extendingbeyond the distal flange 554. The cutting tool guide 550 can becannulated, defining a central longitudinal bore 562 that can receivethe shaft 522 of the spacer guide 520. The cutting tool guide 550 canalso include four longitudinal corner bores or other guiding bores 564that can receive respective drills 546 for drilling four holescorresponding to the corner cylinders 406 b of the implant 400. Theguiding bores 564 can be offset from the central longitudinal bore 562in a direction transverse to the central longitudinal bore 562. It willbe appreciated that the number and location of the guiding bores 564 canvary depending on the need to create slots for pegs, keels or otherengagement formations of the implant 400 or 100 with the endplates, asdiscussed above in connection with the spacer guide 520. The distalflange 554 can include two projections 568 defining a holding slot 566for holding the flange 524 of the spacer guide 520 and preventingrotation of the cutting tool guide 550 relative to the spacer guide 520.

When the cutting tool guide 550 is placed over the spacer guide 520, theboss 570 extends along the frame member 526 of the spacer guide 520 andinto the disc space prepared by drilling the central hole with thecannulated drills 540. The boss 570 can be substantially the same sizeas the central hole or smaller. The boss 570 can include guiding grooves572 aligned with the corresponding corner bores 564 for guiding thedrills 546 to drill straight holes into the endplates 84 of vertebralbodies 80. The same drill 546 can be used sequentially to drill all fourholes, or alternatively each hole can be drilled with a new drill bitand the old drill 546 left in the cutting tool guide 550 for stabilityduring the remainder of the drilling. The drill 546 can include a stop548 that can contact the cutting tool guide 550 to stop the drill 546 atthe appropriate depth. The distal member 532 of the spacer guide 520 canprovide a stop for the drills used for the smaller corner holes. Bonedebris can be removed by irrigation and suction. It will be appreciatedthat the shape and location of the guiding grooves 572 can varyaccording to the geometry of the implant, as discussed above inconnection with the guiding bores 564.

After the four holes corresponding to four cylinders 406 b of theimplant 400 have been drilled, the spacer guide 520, the cutting toolguide 550 and drills 546 can be removed from the prepared disc space.Referring to FIGS. 48 and 50, an insertion cannula 580 pre-loaded withthe implant 400 and a tamp or pusher member 600 can be used to insertthe implant 400 into the prepared disc space. Alternatively, theinsertion cannula 580 can be loaded intra-operatively. The insertioncannula 580 can also have markings for alignment. The insertion cannula580 can include a bore 581 that can receive the tamp member 600. Thecannula 580 can include a retainer or clip defined by two compliant arms590 integrally formed on the distal portion of the insertion cannula 580for holding the implant 400. The distal portion of the insertion cannula580 defines a bore portion 584 configured to mate with the implant 400.The bore portion 584 can be defined by five cylindrical surfaces 586 and588, as shown in FIG. 49 for mating with the five cylinders 406 a, 406 bof the implant 400. A small portion of the implant 400 can extend out ofthe bore portion 584 of the insertion cannula 580 for ease in aligningthe implant 400 with the prepared disc space. The distal end of theinsertion cannula 580 can also include guiding flanges 582 for guidingthe implant into the disc space. The distal surface of the insertioncannula 580 excepting the guiding flanges 582 can rest on the anteriorfaces of the vertebral bodies 80.

The tamp member 600 can be used to slide the implant 400 past theintegral clip 588 and into the prepared disc space. The tamp member 600can also be used to perform final seating of the implant 400 afterremoval of the insertion cannula 580. The tamp member 600 can havelength selected for the desired implantation depth. The tamp member 600can include a depth stop member 602 that can contact the proximal end ofthe insertion cannula 580 to indicate that the implant 40 has been fullyseated into the prepared disc space.

The method of implanting the intervertebral implant according to thepresent teachings can be used, at the option of the surgeon, forminimally invasive procedures, using a small incision and removing onlyas much degenerative material as necessary. Accordingly, a decreasedrisk of infection, decreased blood loss, decreased exposure toanesthesia and shorter recovery time can be achieved. Further, themethods of the present teachings include relatively few steps and employsimple instrumentation with appropriate hard stops to avoid potentialinjury to the spinal cord. When instruments of different sizes can beused, those can be color-coded to facilitate selection of theappropriate size. As can be seen from the associated drawings, theinstruments have streamlined outlines that allow them to fit easily intothe operative site and provide visibility of the vertebral bodies 80 andthe surrounding tissues. The vertebral implant is pre-loaded in theinsertion cannula, such that assembling and loading the implant duringthe surgical procedure is avoided.

The foregoing discussion discloses and describes merely exemplaryarrangements of the present invention. One skilled in the art willreadily recognize from such discussion, and from the accompanyingdrawings and claims, that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention.

1. An intervertebral implant comprising: a first component having afirst articulating surface and a first bone engagement surface forengaging a first vertebra; and a second component having a secondarticulating surface and a second bone engagement surface for engaging asecond vertebra adjacent to the first vertebra, wherein the secondarticulating surface contacts and articulatably moves relative to thefirst articulating surface for substantially replicating a naturalspinal movement, wherein the first and second articulating surfaces havesubstantially equal radii of curvature in a coronal plane and differentradii of curvature in a sagittal plane, and wherein the first and secondbone engagement surfaces define an outer surface substantially shaped asan envelope of two intersecting cylinders.
 2. The intervertebral implantof claim 1, wherein each of the first and second bone engagementsurfaces comprises a pair of separate convex end portions connected witha concave intermediate portion.
 3. The intervertebral implant of claim2, further comprising bone engagement formations arranged insubstantially parallel rows on the first and second bone engagementsurfaces.
 4. The intervertebral implant of claim 1, wherein the firstarticulating surface includes a concave portion in the coronal andsagittal plane, and the second articulating surface includes a convexportion in the coronal and sagittal plane.
 5. The intervertebral implantof claim 2, in combination with an insertion cannula preloaded with theintervertebral implant, the insertion cannula defining a longitudinalbore, the longitudinal bore shaped to mate with the outer surface of theimplant.
 6. The combination of claim 5, further comprising a retainerremovably coupled to a proximal end of the insertion cannula, theretainer removably retaining the intervertebral implant within thelongitudinal bore.
 7. The combination of claim 6, wherein the retainerincludes a head and first and second compliant arms extending from thehead, the arms received in a diametrical slot defined at the proximalend of the cannula, the arms engageable to the concave intermediateportions of the intervertebral implant for retaining the intervertebralimplant in the insertion cannula.
 8. An intervertebral implantcomprising: a first component having a first bone engagement surfaceengageable with a first vertebra, and a first articulating surface; anda second component having a second bone engagement surface engageablewith a second vertebra and a second articulating surface, wherein thefirst and second articulating surfaces contact and move relative to oneanother during implantation permitting relative motion between the firstand second vertebrae, wherein the first and second articulating surfaceshave substantially equal radii of curvature in a coronal plane anddifferent radii of curvature in a sagittal plane, and wherein the firstand second bone engagement surfaces define an outer surfacesubstantially shaped as an envelope of two intersecting cylinders whenthe first and second articulating surfaces are in direct contact withone another.
 9. The intervertebral implant of claim 8, wherein each ofthe first and second bone engagement surfaces comprises a pair ofseparate convex end portions connected with a concave intermediateportion.
 10. The intervertebral implant of claim 8, wherein the firstarticulating surface includes a concave portion in the coronal andsagittal plane, and the second articulating surface includes a convexportion in the coronal and sagittal plane.
 11. The intervertebralimplant of claim 8, further comprising bone engagement formationsarranged in substantially parallel rows on the first and second boneengagement surfaces.
 12. The intervertebral implant of claim 9, incombination with an insertion cannula defining a longitudinal bore, thelongitudinal bore shaped to mate with the outer surface of the implant.13. The combination of claim 12, further comprising a retainer removablycoupled to a proximal end of the insertion cannula, the retainerremovably retaining the intervertebral implant within the longitudinalbore.
 14. The combination of claim 13, wherein the retainer includes ahead and first and second compliant arms extending from the head, thearms received in a diametrical slot defined at the proximal end of thecannula, the arms engageable to the concave intermediate portions of theintervertebral implant for retaining the intervertebral implant in theinsertion cannula.
 15. An intervertebral implant comprising: a firstcomponent having a first articulating surface and a first boneengagement surface for engaging a first vertebra; and a second componenthaving a second articulating surface and a second bone engagementsurface for engaging a second vertebra adjacent to the first vertebra,wherein the second articulating surface contacts and articulatably movesrelative to the first articulating surface for substantially replicatinga natural spinal movement, wherein the first articulating surfacecomprises a convex portion in the coronal plane and a concave portion inthe sagittal plane, and the second articulating surface includes aconcave portion in the coronal plane and convex portion in the sagittalplane, and wherein the first and second bone engagement surfaces definean outer surface substantially shaped as an envelope of two intersectingcylinders.
 16. The intervertebral implant of claim 15, wherein in thesagittal plane the curvatures of the respective convex and concaveportions of the first and second articulating surfaces are different.17. The intervertebral implant of claim 15, wherein in the coronal planethe first articulating surface is substantially V-shaped with a roundedtip.
 18. The intervertebral implant of claim 15, further comprising boneengagement formations arranged in substantially parallel rows on thefirst and second bone engagement surfaces.
 19. The intervertebralimplant of claim 15 in combination with an insertion cannula preloadedwith the intervertebral implant, the insertion cannula defining alongitudinal bore, the longitudinal bore shaped to mate with the outersurface of the implant.
 20. The combination of claim 19, furthercomprising a retainer removably coupled to a proximal end of theinsertion cannula, the retainer removably retaining the intervertebralimplant within the longitudinal bore.